1. Field of the Invention
The present invention relates to a color filter substrate of a liquid crystal display (LCD) device and its manufacturing method and, more particularly, to a color filter substrate and its manufacturing method that is capable of preventing degradation of properties of a black matrix by changing a structure of the black matrix.
2. Description of the Background Art
In general, a black matrix of an LCD, positioned at each boundary of color filter layer representing red, green and blue color, interrupts a light at a region which is not controlled by a pixel electrode, so as to improve an overall contrast of the LCD.
Conventional methods for manufacturing a color filter substrate including the black matrix include a method in which chromium or chromium oxide is plated on the upper surface of a glass substrate and patterned, and a method in which a resin is spread on the upper surface of a glass substrate and patterned.
The method of forming a black matrix by using chromium or chromium oxide is adopted in case that the height of the black matrix is relatively low and a color layer is formed by a pigment dispersion method. Meanwhile, the method of forming a black matrix by using a resin is adopted in case that a black matrix is formed relatively high and a color layer is formed by an ink-jet print method.
As mentioned above, in the conventional arts, the pigment dispersion method and the ink-jet method are usually used to form a color layer positioned between black matrices, and such conventional color filter substrate and its manufacturing method will now be described with reference to the accompanying drawings.
FIGS. 1A through 1E are sectional views showing sequential process of manufacturing a lower plate of a general LCD.
As shown in FIGS. 1A through 1E, the manufacturing process of a lower plate of an LCD includes the steps of: plating a metal at an upper surface of a glass substrate 1 and patterning it by a photolithography process so as to form a gate electrode 2; plating a gate insulation film 3 at an upper surface of the gate electrode 2, plating an amorphous silicon at an upper surface of the gate insulation film and patterning it so as to form an active area 4 at an upper side of the gate electrode 2 so that a thin film transistor is to be formed; forming a source electrode 5 and a drain electrode 6 at a certain upper portion of the gate electrode 2, separated with a certain interval from the central portion of the active area 4; plating a passivation layer 7 at an entire upper surface of the resulting structure and forming a contact hole in the passivation film 7 so as to expose a certain upper portion of the drain electrode 6; plating ITO (Indium Tin Oxide) at an entire upper surface of the resulting structure and patterning it so as to form a pixel electrode 8 which is connected to the exposed drain electrode 6 and positioned at an upper side of a region where the thin film transistor is not positioned.
The process of manufacturing a lower plate of an LCD will now be described in detail with reference to FIGS. 1A through 1E.
First, as shown in FIG. 1A, a metal is plated at an upper surface of the glass substrate 1. Next, a photosensitive polymer is spread at an upper surface of the metal, exposed and developed so as to form a pattern exposing a portion of the metal. And then, the exposed metal is etched through an etching process using the photoresist pattern as an etching mask, thereby forming the gate electrode 2 to be positioned at a certain upper portion of the glass substrate 1.
Thereafter, as shown in FIG. 1B, after the gate insulation film 3 is plated at the upper surface of the glass substrate 1, the amorphous silicon is plated on the upper portion of the gate insulation film 3 and patterned through the photolithography process, so as to form the active area 4 at an upper side of the gate electrode 2 where the thin film transistor is to be formed.
And then, as shown in FIG. 1C, the metal is plated at the upper surface of the resulting structure, patterned through the photolithography process so as to form the source electrode 5 and the drain electrode 6 at both sides of the active area 4, separating them as wide as a channel region formed at the center thereof.
And, as shown in FIG. 1D, after the passivation film 7 is plated at the entire upper surface of the resulting structure, the contact hole is formed in the passivation film 7 through the photolithography process, exposing a certain upper portion of the drain electrode 6.
Thereafter, as shown in FIG. 1E, the ITO is plated at the upper surface of the resulting structure and patterned to form the pixel electrode 8 to be connected to the drain electrode 6.
FIGS. 2A through 2D show sectional views of a process of manufacturing an upper plate of an LCD including the conventional color filter substrate.
As shown in FIGS. 2A through 2D, a process of manufacturing an upper plate of an LCD including the conventional color filter substrate includes the steps of: plating a metal or spreading a resin at an upper surface of a glass substrate 21, and patterning the metal or the resin so as to form a black matrix 22 to be formed at a certain upper portion of the glass substrate 21 at a certain distance; forming a color layer 23, a color filter, at an upper portion of the glass substrate 21 exposed between the black matrices 22; forming an over-coating layer at an entire upper surface of the resulting structure to protect the color layer 23; and forming a common electrode 25, a transparent electrode, at an upper surface of the resulting structure.
The conventional method for manufacturing the upper plate of an LCD including the color filter will now be described in detail.
First, as shown in FIG. 2A, a metal such as chromium or chromium oxide is plated or a resin 21 is spread at the upper surface of the glass substrate 21. Next, the metal or the resin is patterned so as to form a black matrix 22 to be positioned at a certain upper portion of the glass substrate 21 at a certain distance.
At this time, the black matrix 22 should have characteristics of excellent adherence and light absorption rate. The black matrix 22 is formed in a grid-typed structure which divides each color layer of the color filter into pixel units on a plane, and each unit black matrix 22 has a single structure that different color layers come in contact with both sides of the unit black matrix 22. In the construction of the lower plate, the grid-typed structure of the black matrix 22 is formed such that it is directed to the upper side of a transistor gate line and an upper side of a data line.
Thereafter, as shown in FIG. 2B, a color layer 23, a color filter, is formed at an upper portion of the glass substrate 21 exposed between the black matrices 22. At this time, the color layers 23 are typically formed in order of red, green and blue color.
The color layer 23 forming methods are roughly divided into a pigment method and a dye method, and, depending on a manufacturing method, it is also divided into a dyeing method, a dispersion method, a spread method, a print method, an ink-jet print method, or the like.
Among them, the pigment dispersion method is widely used in which a photoresist containing a pigment is spread and developed, on which a post baking is performed to form a specific color layer, and then the process is repeatedly performed to sequentially form different color layers.
Thereafter, as shown in FIG. 2C, the over-coating layer 24 is formed at the entire upper surface of the resulting structure to protect the color layer 23. At this time, the over-coating layer 24 is formed by plating an organic film containing acryl.
And then, as shown in FIG. 2D, ITO is plated at the upper surface of the resulting structure and patterned through a photolithography process, so as to form a transparent electrode 25 in the direction of the pixel electrode 8 formed at the lower plate.
FIG. 3 is a flow chart of the process of manufacturing the color filter substrate adopting the pigment dispersion method.
As shown in FIG. 3, the process of manufacturing the color filter substrate adopting the pigment dispersion method includes a series of steps in which chromium is plated on the glass substrate and patterned through a photolithography process so as to form the black matrix, a photoresist containing a color layer component repeatedly for the red, green and blue through coating, exposing, developing and post baking, is placed to be in contact with the glass substrate between the black matrices, and different color layers are formed mutually being in contact with each other at the central portion of the black matrix.
FIGS. 4A through 4D are sequential sectional views of the process of manufacturing the color filter substrate by using the pigment dispersion method.
As shown in FIGS. 4A through 4D, the process of manufacturing the color filter substrate by using the pigment dispersion method includes the steps of: plating chromium at an upper portion of the glass substrate 21; spreading and developing the photoresist (PR) at an upper portion of the chromium (Cr) and exposing a certain upper portion of the plated chromium at regular intervals; etching chromium through an etching process by making the photoresist (PR) pattern as an etching mask and removing the photoresist (PR) pattern so as to form black matrix 22 on the glass substrate 21; and sequentially forming different (R, G, B) color layers 22 between the black matrices 22 by using the pigment dispersion method.
Though the pigment dispersion method consumes a large amount of a material compared to the spin method, it has an excellent uniformity in the thickness, so that it is most widely used.
However, with the pigment dispersion method, the photoresist should be spread, exposed, developed and post-baked for each of the red, green and blue colors, and thus, the manufacturing process is complicated. In addition, a step of spreading the photoresist by the spin-coating method is necessary, the most of the photoresist spread in the development process should be removed, and a high-priced process with much loss of a material, resulting in an increase in a manufacturing cost of a color filter.
Moreover, as the LCD gets larger in its size, it is not easy to obtain a uniformity of the photoresist spread by the spin-coating method. Thus, it can hardly applied for manufacturing the large-scale color filter.
Unlike the pigment dispersion method, the inkjet print method, a color layer forming method, is such that a relatively thick black matrix is formed by using a resin, an ink solution comprising of a color layer component and an organic binder is pressured between the black matrices, and the ink solution is injected from a nozzle and dried to remove the organic binder, thereby attaching the color layer on the glass substrate.
The ink-jet printer method consumes a less amount of material compared to the other methods, so that a manufacturing cost of the color filter can be reduced.
FIGS. 5A through 5D are sequential sectional views showing the process of fabricating a color filter substrate to form a color layer by the ink-jet print method.
As shown in FIGS. 5A through 5D, the process of fabricating a color filter substrate includes the steps of: spreading a resin at an upper portion of the glass substrate 21 and forming a pattern to form a resin black matrix 22 higher than the chromium black matrix, and injecting an ink solution (R) of a specific color between the resin black matrices 22 by using the ink-jet print method; drying the injected ink solution (R) to form a color layer 23 (R); injecting an ink solution (G) with a different color from the color layer 23 (R) between the resin black matrices 22 positioned at the side of the formed color layer 23 (R); and drying the injected ink solution (G) to form a color layer 23 (G).
However, in the conventional process of manufacturing the color filter substrate to form the color layer by the ink-jet print method, in order to obtain a color layer with a desired thickness, a thicker color layer than the resin black matrix 22 should be printed, and accordingly, the injected ink solution can be spread to a different color layer region before it is dried, causing a degradation of an yield.
In addition, as the solvent contained in the ink solution is infiltrated into the resin black matrix 22, it makes the black matrix to lose its repulsive force to the ink solution, resulting in a problem that it is very difficult to form a desired pattern.
FIG. 5B shows that as the solvent contained in the ink solution is infiltrated into the resin black matrix 22 in the process of forming the color layer 23 (R), the repulsive force of the resin black matrix 22 against the ink solution is lost.
In such a state, as shown in FIGS. 5C and 5D, if a different color ink solution (G) is injected, the injected ink solution (G) passes beyond the repulsive force-lost black matrix 22, and in case of drying the ink solution thereafter, a desired color filter can be hardly obtained due to the mixture of the color layers 23.
Thereafter, through the steps as illustrated in FIGS. 2C and 2C, the overcoating layer 24 and the transparent electrode 25 are formed.
FIGS. 6A through 6D are sectional views of the process of attaching the manufactured upper plate and lower plate.
As shown in FIGS. 6A through 6D, the process of attaching the upper plate and the lower plate includes the steps of: forming an orientation film 31 at an upper portion of the upper plate 30, the color filter, rubbing the oriented film 31 by using a rubbing fabric so that liquid crystal can be oriented at a follow-up step, and plating a sealant 32 at a portion other than a display effective area of the upper plate 30; forming an oriented film 34 at an upper portion of the lower plate 33 and rubbing the oriented film 34 by using the rubbing fabric so that liquid crystal can be oriented, and forming a spacer 35 with a uniform distribution on the oriented film 34; facing the upper plate 30 and the lower plate 33 so that the two oriented films 31 and 34 are facing each other, and firing the sealant 32 so as to attach the upper plate 30 and the lower plate 33; and injecting liquid crystal 36 into the region between the upper plate 30 and the lower plate 30 as attached.
The process of attaching the upper plate and the lower plate will now be described in detail.
First, as shown in FIG. 6A, the oriented film 31 is formed at an upper portion of the upper plate 30, the color filter, that is, at the upper portion of the transparent electrode 25. At this time, the oriented film 31 is formed in such a manner that an oriented liquid is uniformly applied on a rubber resin plate attached on a roller, printed on the substrate, dried so that the oriented film 31 can be uniformly spread while evaporating the solvent, dried by a firing process and hardened.
And then, the oriented film 31 is rubbed by using the rubbing fabric. Through the process, the oriented film 31 is formed in a certain direction. Thereafter, the sealant 32 is plated at a portion other than the display effective area of the upper plate 30 by using a screen mask method, printed, and heated for 48 minutes at a temperature of 90° C. to evaporate the solvent.
Thereafter, as shown in FIG. 6b, the oriented film 34 is formed at an upper portion of the lower plate 33, and rubbed by using the rubbing fabric, so as to provide a certain direction in which the liquid crystal is oriented, and then, the spacer 35 is scattered on the oriented film with a uniform distribution.
The spacer 35 serves to maintain a space between the upper plate 30 and the lower plate 33. The scattering methods includes a wet scattering method in which the spacer 35 is mixed with the solvent and scattered and the solvent is evaporated, and a dry scattering method in which the spacer 35 and the lower plate 33 are charged in a different form so as to be scattered without a mass. Among them, the dry scattering method is usually used to position the spacer 35.
Next, the upper plate 30 and the lower plate 33 are placed in the facing manner so that the two oriented films 31 and 34 can be faced each other, and a plastic working is performed on the sealant 32, so as to cohere the upper plate 30 and the lower plate 33.
In the coherence process, the upper plate 30 and the lower plate 33 at not completely sealed but there is formed a liquid crystal injection hole with a portion thereof exposed.
And then, as shown in FIG. 6D, the liquid crystal 36 is injected into the region between the upper plate 30 and the lower plate 33, and the liquid crystal injection hole is sealed to completely separate the liquid crystal from the outside.
FIG. 7 is an operational illustration view of a general LCD.
As shown in FIG. 7, by applying a gate voltage to the gate electrode 2 of the transistor, an operation voltage applied through a data line is applied to the pixel electrode 8 and, at the same time, the direction of the liquid crystal is changed due to a difference voltage between the operation voltage and the transparent electrode 25 of the upper plate, so that a degree of light transmission of the back light 27 is determined for each pixel.
Accordingly, a transmitted light is displayed as a color represented by each color layer 23 and, at this time, light is interrupted at the region between pixels by the black matrix 22, so that a contrast can be improved.
As noted in FIG. 7, the black matrix 22 has a grid structure which discriminates a different and the same color layer by a pixel unit.
As stated above, the pigment dispersion method, that is, the conventional method of manufacturing a color filter substrate of an LCD, has the following problems: First, the manufacturing cost is increased. Second, since the uniformity of the thickness is not obtained, it can't be adopted for a large scale glass substrate, and thus, an LCD with a large scale screen can't be manufactured.
Meanwhile, in case of using the ink-jet print method, in the process of forming the resin black matrix and forming the first color layer between the black matrix, the component of the resin black matrix at the side of the first color layer is changed, and in addition, in the process of forming the second color layer at the region adjacent to the first color layer, the second color layer can be spread toward the upper portion of the first color layer before the first color is dried yet. As a result, the yield is degraded and a reliability of the process is also degraded.